Some people are talking about "The End Of The World As We Know It"...
...personally I've always preferred the "Zombie Apocalypse" turn of phrase.
"When the zombies come..."
That basically covers everything - leaves no room to get derailled by "never gonna happen" - "but it actually could if..." discussions - and let's face it... if you're prepared for the shambling undead hordes, or for PETA releasing Rage infected chimps you're prepared for a blackout when a power station is flooded, a lightning strike overwhelms the grid, some scumbag poisons a resevoir, an epidemic breaks out and other stuff besides.
Heck if you're prepared for zombies all the rest could happen at the same time and you'd be ok. Haha.
My view:
If you've got food in reserve and know what to do in the event of a zombie apocalypse, you've got a buffer of supplies to get you through the first few days while people panic and wonder what's going on. It will keep you away from the supermarkets where thousands of people will be panicing (and fighting) to get what they need. If you want to keep up the "I've got nothing" appearance - you could show up in the street and at the local supermarket complaining about the lack of food and supplement your rations with foraged food (assuming the zombies/angry mobs aren't making it unsafe to go out).
With a buffer of fuel, food and water ou can get your bearings in the situation and take it all in your stride.
The most likely scenario is "the grid going down". Powercuts, problems with the water supply, large fuel strikes and so on would leave most of the affected people in a difficult position. Add weather issues like heavy storms, deep snow flooding and lighting strikes to that and there's definitely scope for needing to manage for at least a few days.
I see little point in stockpiling a food-mountain, if the Zombies do come, eventually you're going to need to go out to forage and hunt anyway, as long as you can get past the first panic without incident you'll be well fed, warm and healthy which will be a lot more than could be said for people with nothing stored and ready for the apocalypse.
As it happens - I've actually got very little in reserve for when the zombies come - but the subject definitely intests me.
What happened in the wake of Hurricane Katrina should tell us a lot about how much we can rely on the authorities in a "****" scenario, although there's an extra layer of beurocracy that slowed down the response there (the federal government couldn't do anything until the mayor asked them to - and it took a long time for that to happen - that wouldn't be an issue in the UK).
I think self reliance is the best plan in the event of any form of fast or slow moving undead invasion.